Digital imaging systems are used to create two-dimensional and three-dimensional images of objects for reverse engineering, prototyping, computer modeling, animation, graphics applications, inspecting parts, medical procedures, prosthetic device manufacturing and other applications. In prosthetic device manufacturing, for example, an anatomical feature of a specific patient may be digitized to manufacture a custom prosthetic device that comfortably fits the patient. Several digitizing devices and processes are currently available to generate three-dimensional images of objects.
One type of existing digitizing system is a full-contact, free-motion digitizer that has a hand-held probe with a receiver that detects the position of the probe relative to a position reference magnetic field generated by a transmitter. In prosthetic device manufacturing applications, the size and shape of a patient's limb or other anatomical feature is measured by pressing the probe against the patient's skin and scanning the probe over the anatomical feature. The motion tracking system computes the position and orientation of the probe as it moves over the patient's skin to generate a three-dimensional image of the patient's limb. However, because the probe presses against the patient's skin, one problem with the hand-held probe is that it may deflect the skin and produce inaccurate data points that do not correspond to the true size and shape of the patient's limb. As a result, a prosthetic device manufactured according to the data generated by the probe may not comfortably fit the patient. Another problem with this system is that the target object must remain stationary as it is scanned by the probe to prevent inaccurate measurements. Consequently, many medical patients become uncomfortable and may even experience pain during the digitization process because they must remain still for relatively long periods of time.
Another existing digitizing system is a noncontact, restricted-motion digitizer that has a support structure with a guide track, a noncontact displacement sensor mounted to the support structure to travel along the guide track, and a brace to fixedly hold a target object during digitizing. Alternatively, the displacement sensor may be attached to a mechanical arm. The noncontact displacement sensor is generally a laser distance measuring device that measures the displacement between the sensor and the surface of the target object, and the position of the sensor is detected by denoting its position on the guide track or on the mechanical arm. In prosthetic device manufacturing, a patient's limb is strapped to the brace and fixed in place, and the displacement sensor moves along the guide track and scans the patient's limb with a laser beam. The distance measurements from the laser and the position of the laser are correlated by a computer to calculate the surface points of the target object and generate a three-dimensional image.
Although noncontact, restricted-motion digitizers do not deflect the skin of a patient, they are generally large, complex pieces of equipment with many mechanical parts. Moreover, the guide track or the mechanical arm may also restrict the motion of the displacement sensor and prevent the laser beam from scanning portions of the target object. Thus, as with conventional full contact digitizers, patient's are generally uncomfortable or even in pain during the digitizing process because they must hold still while being scanned with the laser.